1. Technical Field
The present invention relates to a printing device used in a facsimile machine, a copying machine, and office automation equipment, a printing device control program, and a printing device control method, and more particularly, to a so-called ink-jet printing device configured to draw specific characters and images by ejecting fine particles of liquid inks of several colors onto a print sheet (recording member), a printing device control program, a printing device control method, a print data generation device, a print data generation program, and a print data generation method.
2. Related Art
Hereinafter, a printing device, in particular, a printer adopting the ink jet method (hereinafter, referred to as an ink-jet printer) will be described.
Ink-jet printers have been used extensively among not only offices but also general users as personal computers and digital cameras have come into widespread use because they are generally inexpensive and high-quality color printed matter can be obtained easily.
An ink-jet printer normally produces desired printed matter by moving a mobile body, called a carriage and provided with an ink cartridge and a print head in a single-piece design, to reciprocate over a medium used for printing (for example, a print sheet) in a direction perpendicular to the paper transportation direction, and simultaneously ejecting (discharging) dot-shaped particles of liquid inks from the nozzles provided to the print head to draw specific characters and images on the medium. By providing the carriage with ink cartridges of four colors including black (black, yellow, magenta, and cyan) and the print heads for respective colors, not only monochrome printing but also full color printing can be readily executed by combining the respective colors (color printing of six, seven, or eight colors is now available by using light cyan, light magenta, etc. in addition to the four colors).
In an ink-jet printer of a type that executes printing by moving the print heads on the carriage to reciprocate in a direction perpendicular to the paper transportation direction, the print heads have to reciprocate several tens to a hundred times or more to clearly print a full page. Hence, it has a drawback that printing takes a considerably long time in comparison with a printing device adopting another method, such as a laser printer using electrophotographic technology such as in a copying machine.
Meanwhile, an ink-jet printer of a type that omits the carriage by disposing a long print head of a size comparable to (or larger than) the width of the print sheet is known. Because there is no need to move the print head in the width direction of the print sheet in this ink-jet printer, a so-called single-scan (1-pass) printing can be achieved, which in turn enables printing as fast as a laser printer. In addition, the carriage to mount the print heads thereon and a driving system to move the carriage can be omitted. The housing of the printer can therefore be reduced in size and weight; moreover, there is another advantage that the printer becomes remarkably quiet. Incidentally, the ink-jet printer of the firstly-mentioned type is generally referred to as “a multi-pass printer”, and the ink-jet printer of the secondly-mentioned type is generally referred to as “a line-head printer” or “a serial printer”.
The print head indispensable to the ink-jet printer is provided with fine nozzles having a diameter of about 10 to 70 μm that are aligned at regular intervals in one line or in lines in more than one row along the printing direction. This configuration, however, may possibly give rise to a so-called flight deviation (or flight bend) phenomenon, which is an event that the ink ejecting direction of a part of the nozzles is inclined due to a manufacturing error or the landing position of a dot formed by a given nozzle is displaced from the ideal position because this nozzle is disposed at a position displaced from the ideal position. In addition, the characteristic varies from nozzle to nozzle, and for a nozzle having a considerable variance, a quantity of ink becomes too large or too small in comparison with an ideal quantity.
Defective printing referred to as the so-called banding (streak) phenomenon thus occurs in a portion printed by such failing nozzles, which possibly deteriorates the printing quality. In other words, once the flight deviation phenomenon occurs, a distance between dots ejected from adjacent nozzles becomes uneven. In a portion where the distance between adjacent dots becomes larger than usual, a white streak (when a print sheet is white) occurs, and in a portion where the distance between adjacent dots becomes smaller than usual, a dark streak occurs. Also, when the value of a quantity of ink does not coincide with the ideal value, a dark streak occurs in a portion printed by a nozzle having a larger quantity of ink and a white streak occurs in a portion printed by a nozzle having a smaller quantity of ink.
In particular, the banding phenomenon noticeably occurs more readily with a line-head printer in which the print head or a medium used for printing is fixed (1-pass printing) than with the multi-pass printer (serial printer) (for the multi-pass printer, a technique has been devised to make the banding less noticeable by exploiting its configuration to move the print head to reciprocate a number of times).
Such being the case, studies and developments have been conducted assiduously for hardware, such as improvements in the manufacturing technique and improvements in the design of the print head, to prevent a kind of defective printing caused by the banding phenomenon. However, it is difficult to provide a print head that is 100% free from the banding phenomenon because of the limits to hardware improvement due to manufacturing costs and current technical abilities.
Hence, as a technique for suppressing the banding phenomenon, printing control by software as described below is now used in addition to the improvements in the hardware as described above.
According to a first technique disclosed in the related art, for example, in JP-A-2002-19101 and JP-A-2003-136702, variances among nozzles and an ink ejection failure are addressed as follows. That is, variances among heads are addressed using a shading correction technique in a less dense portion, whereas the banding or variances are made less noticeable using an alternate color to the original color (for example, in the case of printing in black, cyan or magenta is used as an alternate color to black) in a dense portion.
According to a second technique disclosed in the related art, for example, in JP-2003-63043, a quantity of ejected ink is increased for adjacent nozzles corresponding to pixels in the neighborhood of a non-ejecting nozzle for a solid image (an image portion having a relatively large area in comparison with a line image, and it is a region densely covered with ink; however, there may be a case where it is not fully covered due to an edge effect), so that a solid image is formed using the nozzles as a whole.
According to a third technique disclosed in the related art, for example, in JP-A-5-30361, the banding phenomenon is avoided by absorbing a variance in the quantity of ink ejected from the nozzles by feeding back a quantity of variance in each nozzle to error diffusion.
According to a fourth technique disclosed in the related art, for example, in JP-A-2004-58284, assuming that there is a nozzle (N) under an abnormal ink ejection condition, record data corresponding to this failing nozzle (N) is appended to record data corresponding to neighboring nozzles (N−1) and (N+1) positioned in the neighborhood of the failing nozzle (N). The banding phenomenon can be avoided by compensating for the record data corresponding to the abnormal nozzle (N) in this manner.
However, the first technique in the related art for suppressing the banding phenomenon and variances using another color has a problem that the hue changes in a portion where this technique is applied. This technique is therefore unsuitable for printing that requires a high image quality and a high quality, such as printing of a color picture image.
In addition, when the method of avoiding the white streak phenomenon by distributing the information about the non-ejecting nozzle to nozzles on the right and left is adopted as a countermeasure against the flight deviation phenomenon, it is indeed possible to reduce a white streak; however, there is a problem that banding still occurs in a dense portion.
The second technique in the related art has no problem when a solid image is produced as printed matter. However, this technique cannot be used when halftone printed matter is produced. In addition, the method of filling fine lines using another color has no problem for use to a limited extent. However, for an image on which the color used as an alternate color is used continuously, the hue changes in part of the image. This technique therefore has the same problem as the first technique in the related art.
The third technique in the related art has difficulty solving a problem that the dot formation content has discrepancies, because complicated processing is required to enable appropriate feedback for solving such a problem.
The fourth technique in the related art has a problem that in a case where dots of different sizes are formed using nozzles in the neighborhood in the downstream processing after binarization, when the dots have a γ characteristic, there is a risk that the area grayscale is lost in the portion where this technique is applied.